Phosphate optical glass with positive anomalous partial dispersion

ABSTRACT

NOVEL OPTICAL GLASSES ARE DISCLOSED WHICH POSSESS A POSITIVE ANOMALOUS PARTIAL DISPERSION AND WHICH ARE RESISTANT TO CHEMICAL INFLUENCES, FOR EXAMPLE FROM THE ATMOSPHERE, TO SUCH A DEGREE THAT LENSES MANUFACTURED FROM THESE GLASSES CAN BE EMPLOYED AS FRONT LENSES IN OPTICAL SYSTEMS, SUCH AS PHOTOGRAPHIC OBJECTIVES,ACCORDING TO TO THE INVENTION THE GLASSES ARE MELTED FROM A BATCH COMPOSITION CONSISTING ESSENTILALLY OF:   5-20% BY WEIGHT OF THE METAPHOSPHATES OF THE ALKALINE ELEMENTS; 50-75% BY WEIGHT OF A CONSTITUENT SELECTED FROM A GROUP CONSISTING OF THE METAPHOSPHATES OF THE ALKALINE EARTH ELEMENTS MAGNESIUM, CALCIUM, STRONTIUM AND BARIUM; 2-15% BY WEIGHT OF TITANIUM DIOXIDE; AND 2-15% OF THE OXIDE OF BERYLLIUM.

3,597,245 PHOSPHATE OPTICAL GLASS WITH POSITIVE AN OMALOUS PARTIALDISPERSION Heinz Bromer, Hermannstein, Kreis Wetzlar, and NorbertMeinert and Johann Spincic, Wetzlar, Germany, assignors to Ernst LeitzG.m.b.H., Wetzlar, Germany No Drawing. Continuation of application Ser.No.

768,915, Oct. 18, 1968. This application May 12,

1970, Ser. No. 37,414 Claims priority, application Germany, Oct. 28,1967,

P 15 96 888.4 Int. Cl. C03c 3/00 U.S. Cl. 106-47Q 6 Claims ABSTRACT OFTHE DISCLOSURE Novel optical glasses are disclosed which possess apositive anomalous partial dispersion and which are resistant tochemical influences, for example from the atmosphere, to such a degreethat lenses manufactured from these glasses can be employed as frontlenses in optical systems, such as photographic objectives, According tothe invention the glasses are melted from a batch composition consistingessentially of:

20% by weight of the metaphosphates of the alkaline elements; 50-75% byweight of a constituent selected from a group consisting of themetaphosphates of the alkaline earth elements magnesium, calcium,strontium and barium; 215% by weight of titanium dioxide; and 2-15 ofthe oxide of beryllium.

CROSS-REFERENCE TO RELATED APPLICATIONS This is a continuation ofcopending application, Ser. No. 768,915, filed Oct. 18, 1968, and nowabandoned.

Reference is made to copending application Ser. No. 542,035, filed Apr.12, 1966, now Pat. No. 3,451,829 by two of the three inventors of thepresent invention and assigned to the same assignee.

BACKGROUND OF THE INVENTION (1) Field of the invention The presentinvention pertains to glass, more particularly to optical glasses havinganomalous partial dispersion.

(2) Description of the prior art Optical glasses having anomalouspartial dispersion are well known to those skilled in the art of meltingglass and also to the designers of lenses and optical systems.

For the lens designer these glasses are particularly important ifobjectives with a corrected secondary spectrum are to be calculated. Inpatent application Ser. No. 542,035 the employment of such glasses isdisclosed in more detail. The patent application referred to relatesparticularly to glasses having a positive deviation of the partialdispersion which is usually designated by the A, valuefrom the curve fornormal glasses in the Er V -diagram.

The glasses disclosed in application Ser. No. 542,035 consist of thephosphates of aluminum and of the phosphates of the alkaline earthelements as the glass former. Additionally, they contain alkaline oxidesand oxides of bivalent elements and, further, they may contain titaniumdioxide of which it is known that it contributes essentially to apositive deviation of the partial dispersion.

As mentioned before, these known glasses possess properties with regardto their anomalous partial dispersion which are most valuable for thedesigner of lens systems, objectives etc. However, owing to theirsensitivity towards nited States Patent Oce I 3,597,245 Patented Aug. 3,1971 chemical and atmospherical influences they are not fit to be usedas the front or rear lens in such a system.

SUMMARY OF THE INVENTION It is, therefore, the object of the inventionto provide optical glasses also having a positive anomalous partialdispersion, just as have the glasses disclosed in application Ser No.542,035, which inventive glasses, however, are resistant to chemicalinfluences to such a degree that lenses manufactured therefrom can beemployed as the front or rear lens in any lens system.

According to the invention these glasses are melted from a batchcomposition consisting of:

5-20 mole percent of the metaphosphates of the alkaline elements; 50-75%by weight of the metaphosphates of the alkaline earth elementsmagnesium, calcium, strontium and/0r barium; 2-15% by weight of titaniumdioxide; and 2-15% of the oxide of beryllium.

The foregoing composition can also be defined by the mole percentage, inwhich case the percentage would be as follows:

6-20 mole percent of the metaphosphates of the alkaline elements;

25-27 mole percent of the metaphosphates of the alkaline earth elementsmagnesium, calcium, strontium and/or barium;

3-20 mole percent of titanium dioxide; and

10-50 mole percent of the oxide of beryllium.

For adjusting the optical values the oxides of the alkaline earthelements magnesium, calcium, strontium and barium can be used. In orderto achieve proper decolorization as well as to render the batchcomposition easy to melt the arsenate of potassium (KAsO and/ or thefluorotitanate of potassium (K TiF can be added.

The improvement of the chemical resistance of the glasses is largely dueto the oxide of beryllium which is included in the batch composition.This constituent is generally considered undesirable in a batchcomposition owing to its poisonous nature. However, it has been foundthat beryllium oxide can be handled safely if adequate precautions aretaken and certain safety measures are observed. Such safety measuresshould, for example, include an exhauster at the working place and dustface shields for the men mixing the batch composition. During themelting process the beryllium is transformed to other clremicalcompounds, thereby losing its toxicity.

DESCRIPTION OF THE APPENDING TABLES In the following tables are listedseveral examples for glasses according to the invention. Moreparticularly, Table 1 includes examples wherein by variation of thepercentage of metaphosphate or by variation of the percentage of theoxide of barium in the batch composition a variation of the refractiveindex (n) and the partial dispersion values (Av) has been achieved,while the dispersion of value (v) remains unchanged.

Table 2 includes examples wherein the percentage of the oxide ofberyllium has been lowered while the percentage of titanium dioxide hasbeen increased. Here, it is readily discernible that corresponding tothe reduced percentage of titanium dioxide also the Av values decrease.On the other hand, it is this way easily possible to achieve majorvariations with regard to the refractive indices (n) and the dispersionvalues (v).

In Table 3 are listed glasses which possess equal Av values whichglasses, however, show variations of the refractive index (n) and of thedispersion values (v). This being the result of an increase inpercentage of the oxide of barium, while, at the same time, thepercentage of the oxide of beryllium was reduced.

3 DESCRIPTION OF THE MELTING OF A 50 g. BATCH COMPOSITION The well-mixedbatch is in portions put into the crucible at a temperature of 1400 C.Thereafter, the batch is melted for 40 minutes and is then cast intosteel molds O or into non-ferrous molds pre-heated to 450 C.

TAB LE 1 Batch composition N 1 2 3 4 5 6 1 8 9 10 LiPOaI Weight percent7. 4 7. 4 7. 4 7. 4 7. 4 7. 4 7.4 7. 4 7. 4 7. 4 Mole percent 8. 48 8. 58. 5 8. 7 .6 8. 7 8.8 8. 4 18. 6 S. 9 KPO3Z Weight percent 10. 0 7. 0 4.0 5.0 10.0 5. 0 Molepercent 8.37 5.8 3.5 4.2 8.3 4.2

ZMePOg:

Weight percent 17. 4 14. 4 11.4 7. 4 12. 4 7. 4 7. 4 17. 4 12. 4 7. 4Mole percent 16.85 14.3 12.0 8. 7 12. 8 .7 8.8 16. 7 12. s 8 9 Weightpercent 50.0 50. 0 50. 0 50.0 50.0 50.0 60. 0 50. 0 50. 0 50, (1 Molepercent 27. 2 2T. 2 27. 4 27. 6 27.7 27. 9 33. 6 26. 6 27. 8 2s. 7C3.(PO3)2I Weight percent 14. 6 14. 6 14.6 14. 6 19. 6 24. 6 14. 6 4. 614.6 14 6 Mule percent 7. 3 7. 4 7. 4 7. 5 10.0 12. 5 7. 5 2. 2 7. 5 7.7 Ba(POa)z:

Weight percent 5.0 10, 0 Mole percent 1. 6 3. 5

EMe(POa) Weight percent 64. 4 64. 6 64. 6 64. 6 69. 6 74. 6 74. 6 54. 669. 6 74. 6 Mole percent 34. 5 34. 6 34.8 35. 1 37. 7 40. 4 41. 1 28. S36. 9 39. 9

Weight percent 7. U 7.0 7.0 7.0 7. 0 7. 0 7.0 7.0 7. O I, 0 B OMolepercent S. 65 .7 8. 7 8. 8 8. 7 8. 8 8. 9 .5 8. 7 1.0

Weight percent 10. 0 10.0 10. 0 19. 0 10. 0 10.0 10. 0 10.0 10. 0 10, 0Mole percent 39. 4 39. 8 40. O 40. 3 40. Z 41. 5 40. 6 39. 0 41. 0 41, 6a0:

Weight percent- 3. 0 6. 0 10. 0 10. 0 Mole percent- 2. 0 3. 9 6. 5 6. 4KASOgZ Weight percent 1.0 1.0 1.0 1.0 1. 0 1.0 .1. 0 1.0 1.0 1.0 Molepercent. 0. 6 0. 6 0. 6 0. 6 0. 6 0.6 0.6 0.6 0.6 0. 6 1. 5993 1.6050 1. 6127 1. 60114 1 6058 1. 6071 1 6064 1. 6115 44. 5 44. 6 44. 744. 5 44. 7 45. 4 44. 2 44. 1 5169 5154 5146 5132 5250 5202 5113 5137+8.6 +8.3 +7.8 +6.4 +15.1 +124 +5.0 +6.6

TABLE 3 Batch composition N 0 16 17 18 LiPOg: TABLE 2 Weight percent 8.28. 2 8. 2 8. 2 5 Mole percent-................ 9.6 10.7 12.1 13.7 Batchcomposition 3 NO 11 12 13 1 1 15 Weight percent Mole percent LiPOatWeight percent- 7. 4 7. 4 7. 4 7. 4 7.4 B M 1 03: Mole percent 10.1 9. 59. (i 8.1 7. 7 E 11- D 8. 2 8. 2 8. 2 8. 2 KP03. Molepercent................ 9.6 19.7 12.1 13.7 Weight percent. 10. 0 10.010. 0 10. 0 10.0 Mole percent 10.0 9. 4 8. 9 8. c 7. 5 MgtPOahi Weightpercent 54.8 54. 8 54. 8 54. 8 Z MeP0 Mole pe1'ce11t. 30. 4 33. 6 38.144 0 Weight percent. 17. 4 17.4 17. 4 17. 4 17. 4 Ca(PO 3}1: M l percent20.1 18. 9 17. 9 16.1 15. 2- Weight percent 16. 2 16. 2 16. 2 16. 2 Malepercent 8.3 9. 2 10. 4 11. 9 Mg (POa)2Z Weight percent- 50.0 50. O 50.050. 0 50. 0 2 Me (170:1)2: Mole percent. 32.4 30.4 28. 6 25. 6 24. 4Weight percent. 71.0 71. 0 71. 0 71 0 0 7F03 Mole percent 38. 7 42. 848. 5 55. 9

Weight percent 14. 6 14.6 14.6 14. 6 14. 6 Mole percent.. 8. 7 8. 2 7.86. 9 6.6 T102:

Weight percent '2. 9 2. 9 2. 9 2. 9 2; Mc(POa)22 Mole percent 3.6 4. 04.6 5. 2

Weight percent- 64. 6 64. 6 64. 6 64. e 64. a 60 1350: Molepercent...... 41. 1 3S. 6 36. 4 32. 5 31.0 Weight percent 11.1 8.1 5. 12. 1 Mole percent 45. O 36. 7 25. 9 12. 2 T102: B 5.0:

Weight percent- 13. 0 11.0 9. 0 5. 0 3. 0 Weight percent 3.0 6. U 9. 0M010. percent..... 19. 2 15.3 11. 7 5. 8 3. 3 Mole percent 2.3 5.0 8. 5B50: KAsOs:

Weight percent- 4.0 6.0 8.0 12.0 14. 0 Weight percent 1. 1 1.1 1.1 1. 1Mole percent- 18. 9 26. 5 33. 4 45. 0 50. O Mote percent 6. 7 0.8 0.9 1. 0 KAsOa: KzTiFuz Weight percent. 1.0 1. 0 1.0 1.0 1. 0 Weightpercent 5. 7 5.7 5. 7 5. 7 Mole percent 0.7 0. 7 0.6 0.6 O. 5 2. 4 2. 73.0 3. 5 1. 6406 1. 6262 1. 6119 1.5893 1. 5744 779 1. 5871 1. 5908 1.5907 33. 6 36. 7 40. 4 48.1 55. (i 4. 2 48. 7 46. 8 47. 6 5, 357 5,3205,188 5. 082 4. J66 F 5,100 5.127 5,117 +11.6 6.5 +4.1 +6. 15 +8.6 +8.1)+8.7

We claim:

1. Glass for optical purposes having positive anomalous partialdispersion between about 4.115.1 Av which glass is melted from a batchcomposition consisting essentially of about: 7.417.4% by weight of themetaphosphates of alkaline elements, 54.674.6% by weight of aconstituent selected from a group consisting of the metaphosphates ofthe alkaline earth elements magnesium, calcium and barium, 29-13% byweight of the oxide of titanium, and 21-14% by weight of the oxide ofberyllium.

2. Glass according to claim 1, wherein the batch composition from whichsaid glass is melted consists additionally of up to 7% by weight of aconstituent selected from a group consisting of the arsenate ofpotassium (KAsO and the fluorotitanate of potassium (K TiF 3. Glass asdefined in claim 1, wherein the batch composition from which said glassis melted consists additionally of up to 10% by weight of the oxide ofbarium.

4. Glass according to claim 3, wherein the batch com position from whichsaid glass is melted consists essentially of the following constituents:

Weight percent LiPO 7.4-8.2

KPO 0-10 (with the total of MePO ranging betweeen Mg(PO C3-(PO3)2B3.(PO3)2 (with the total of Me(PO ranging between 6 TiO 2.4-13 BeO2.1-14 BaO 0-10 (with the total of MeO ranging between KAsO 1.0-1.1 KTiF 0-6 5. Glass as defined in claim 3, wherein the batch compositionfrom which said glass is melted consists of about 3.010.0% by weight ofthe oxide of barium.

6. Glass as defined in claim 2, wherein said arsenate of potassium isabout 1.0-1.l% by weight and said fluorotitanate of potassium is about5.7% by Weight.

OTHER REFERENCES Vol. f, M.B.: Technical Glasses; London, 1961, pp. 410-412.

Vol. b, M.B.: Technical Glasses; London, 1961, pp. 410-4l2.

HELEN M. MCCARTHY, Primary Examiner W. R. SATTERFIELD, AssistantExaminer

